1.3.5 Terrestrial biological systems
Plants and animals can reproduce, grow and survive only within specific ranges of climatic and environmental conditions. If conditions change beyond the tolerances of species, then they may respond by:
1. shifting the timing of life-cycle events (e.g., blooming, migrating),
2. shifting range boundaries (e.g., moving poleward) or the density of individuals within their ranges,
3. changing morphology (e.g., body or egg size), reproduction or genetics,
4. extirpation or extinction.
Additionally, each species has its unique requirements for climatic and environmental conditions. Changes, therefore, can lead to disruption of biotic interaction (e.g., predator/prey) and to changes of species composition as well as ecosystem functioning. Since the TAR, the number of studies finding plants or animals responding to changing climate (associated with varying levels of confidence) has risen substantially, as has the number of reviews (Hughes, 2000; Menzel and Estrella, 2001; Sparks and Menzel, 2002; Walther et al., 2002; Parmesan and Galbraith, 2004; Linderholm, 2006; Parmesan, 2006).
Besides climate affecting species, there are many different types of non-climate driving forces, such as invasive species, natural disturbances (e.g., wildfires), pests, diseases and pollution (e.g., soluble-nitrogen deposition), influencing the changes exhibited by species. Many animal and plant populations have been under pressure from agricultural intensification and land-use change in the past 50 years, causing many species to be in decline. Habitat fragmentation (Hill et al., 1999b; Warren et al., 2001) or simply the absence of suitable areas for colonisation, e.g., at higher elevations, also play an important role (Wilson et al., 2005), especially in species extinction (Williams et al., 2003; Pounds et al., 2006).